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Rainfall-induced landslides are a common and significant source of damages and fatalities worldwide. Still, we have little understanding of the quantity and properties of landsliding that can be expected for a given storm and a given landscape, mostly because we have few inventories of rainfall-induced landslides caused by single storms. Here we present six new comprehensive landslide event inventories coincident with well identified rainfall events. Combining these datasets, with two previously published datasets, we study their statistical properties and their relations to topographic slope distribution and storm properties. Landslide metrics (such as total landsliding, peak landslide density, or landslide distribution area) vary across 2 to 3 orders of magnitude but strongly correlate with the storm total rainfall, varying over almost 2 orders of magnitude for these events. Applying a normalization on the landslide run-out distances increases these correlations and also reveals a positive influence of total rainfall on the proportion of large landslides. The nonlinear scaling of landslide density with total rainfall should be further constrained with additional cases and incorporation of landscape properties such as regolith depth, typical strength or permeability estimates. We also observe that rainfall-induced landslides do not occur preferentially on the steepest slopes of the landscape, contrary to observations from earthquake-induced landslides. This may be due to the preferential failures of larger drainage area patches with intermediate slopes or due to the lower pore-water pressure accumulation in fast-draining steep slopes. The database could be used for further comparison with spatially resolved rainfall estimates and with empirical or mechanistic landslide event modeling.

PurposeSpectrocolourimetric measurements provide a relatively inexpensive, quick and non-destructive alternative to the analysis of geochemical and organic matter properties. When used in the analysis of sediments and their potential sources, these colour parameters may provide important information on the dominant processes (i.e. erosion) occurring in the Critical Zone. Here, they are used to investigate whether eroded sediment is derived from forest (i.e. natural), cultivated (i.e. anthropogenic) or subsoil sources in order to assess their potential to monitor the effect of decontamination in regions impacted by fallout from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident.Materials and methodsFifteen spectrocolourimetric properties (L*, a*, b*, C*, h, x, y, z, L, a, b, u*, v*, u’, v’) were measured in potential source (n = 37) and sediment (n = 400) samples collected during 13 campaigns from 2011 to 2017 after major flood events in two catchments (total surface area of 450 km2) draining the main FDNPP radioactive pollution plume. Potential sources included topsoil from forest and cultivated sources along with subsoil material originating from landslides, channel banks and the decontamination of cultivated areas. The optimum set of parameters used in the mixed linear model to calculate the sediment source contributions was obtained through the use of a range test, the Kruskal–Wallis H test and a linear discriminant analysis.Results and discussionNine selected colour parameters correctly classified 100% of the source samples (i.e. forest, subsoil and cultivated sources). The results illustrate that cultivated landscapes were the main source of sediment to these river systems (mean 56%, SD 34%) followed by subsoil (mean 26%, SD 16%) and forest sources (mean 21%, SD 24%). However, these contributions varied strongly over time, with a peak of subsoil contributions (mean 57%, SD 17%) in Fall 2015, coinciding with the occurrence of a typhoon after the remediation works. These results were consistent with monitoring studies conducted in the same area that showed the major impact of typhoon Etau in September 2015 on sediment and radiocaesium fluxes.ConclusionsThese original results demonstrate that spectrocolourimetric measurements may contribute to the routine monitoring of the effectiveness of remediation works in this post-accidental context. Owing to the inexpensive, rapid and non-destructive analyses, spectrocolourimetric-based tracing methods have significant potential to provide information on the dominant erosion processes occurring in the Critical Zone.

Quasi-static numerical simulations of slip along a fault interface characterized by multiscale heterogeneity (fractal patch model) are carried out under the assumption that the characteristic distance in the slip-dependent frictional law is scale-dependent. We also consider slip-dependent stress accumulation on patches prior to the weakening process. When two patches of different size are superposed, the slip rate of the smaller patch is reduced when the stress is increased on the surrounding large patch. In the case of many patches over a range of scales, the slip rate on the smaller patches becomes significant in terms of both its amplitude and frequency. Peaks in slip rate are controlled by the surrounding larger patches, which may also be responsible for the segmentation of slip sequences. The use of an explicit slip-strengthening-then-weakening frictional behavior highlights that the strengthening process behind small patches weakens their interaction and reduces the peaks in slip rate, while the slip deficit continues to accumulate in the background. Therefore, it may be possible to image the progress of slip deficit at larger scales if the changes in slip activity on small patches are detectable.

Extant African great apes and humans are thought to have diverged from each other in the Late Miocene. However, few hominoid fossils are known from Africa during this period. Here we describe a new genus of great ape (Nakalipithecus nakayamai gen. et sp. nov.) recently discovered from the early Late Miocene of Nakali, Kenya. The new genus resembles Ouranopithecus macedoniensis (9.6-8.7 Ma, Greece) in size and some features but retains less specialized characters, such as less inflated cusps and better-developed cingula on cheek teeth, and it was recovered from a slightly older age (9.9-9.8 Ma). Although the affinity of Ouranopithecus to the extant African apes and humans has often been inferred, the former is known only from southeastern Europe. The discovery of N. nakayamai in East Africa, therefore, provides new evidence on the origins of African great apes and humans. N. nakayamai could be close to the last common ancestor of the extant African apes and humans. In addition, the associated primate fauna from Nakali shows that hominoids and other non-cercopithecoid catarrhines retained higher diversity into the early Late Miocene in East Africa than previously recognized.

An International Ocean Discovery Program (IODP) workshop was held at Sydney University, Australia, from 13 to 16 June 2017 and was attended by 97 scientists from 12 countries. The aim of the workshop was to investigate future drilling opportunities in the eastern Indian Ocean, southwestern Pacific Ocean, and the Indian and Pacific sectors of the Southern Ocean. The overlying regional sedimentary strata are underexplored relative to their Northern Hemisphere counterparts, and thus the role of the Southern Hemisphere in past global environmental change is poorly constrained. A total of 23 proposal ideas were discussed, with ∼ 12 of these deemed mature enough for active proposal development or awaiting scheduled site survey cruises. Of the remaining 11 proposals, key regions were identified where fundamental hypotheses are testable by drilling, but either site surveys are required or hypotheses need further development. Refinements are anticipated based upon regional IODP drilling in 2017/2018, analysis of recently collected site survey data, and the development of site survey proposals. We hope and expect that this workshop will lead to a new phase of scientific ocean drilling in the Australasian region in the early 2020s.

The last 60 years has seen unprecedented groundwater extraction and overdraft as well as development of new technologies for water treatment that together drive the advance in intentional groundwater replenishment known as managed aquifer recharge (MAR). This paper is the first known attempt to quantify the volume of MAR at global scale, and to illustrate the advancement of all the major types of MAR and relate these to research and regulatory advancements. Faced with changing climate and rising intensity of climate extremes, MAR is an increasingly important water management strategy, alongside demand management, to maintain, enhance and secure stressed groundwater systems and to protect and improve water quality. During this time, scientific research—on hydraulic design of facilities, tracer studies, managing clogging, recovery efficiency and water quality changes in aquifers—has underpinned practical improvements in MAR and has had broader benefits in hydrogeology. Recharge wells have greatly accelerated recharge, particularly in urban areas and for mine water management. In recent years, research into governance, operating practices, reliability, economics, risk assessment and public acceptance of MAR has been undertaken. Since the 1960s, implementation of MAR has accelerated at a rate of 5%/year, but is not keeping pace with increasing groundwater extraction. Currently, MAR has reached an estimated 10 km3/year, ~2.4% of groundwater extraction in countries reporting MAR (or ~1.0% of global groundwater extraction). MAR is likely to exceed 10% of global extraction, based on experience where MAR is more advanced, to sustain quantity, reliability and quality of water supplies.

We present a series of controlled fluid injection experiments in the laboratory on a pre‐stressed natural rough fracture with a high initial permeability (∼10−13 m2) in granite using different fluid pressurization rates. Our results show that fluid injection on a fracture with a slight velocity‐strengthening frictional behavior exhibits dilatant slow slip in association with a permeability increase up to ∼41 times attained at the maximum slip velocity of 0.085 mm/s for the highest‐rate injection case. Under these conditions, the slip velocity‐dependent change in hydraulic aperture is a dominant process to explain the transient evolution of fracture permeability, which is modulated by fluid pressurization rate and fracture surface asperities. This leads to the conclusion that permeability evolution can be engineered for subsurface geoenergy applications by controlling the fluid pressurization rate on slowly slipping fractures. Plain Language Summary Understanding the evolution of fracture permeability during hydraulic stimulation of subsurface reservoirs is the key to characterizing fluid transport and formulating strategies to limit induced seismicity. Accordingly, there is a significant interest in deciphering how the fluid pressurization rate, a constitutive operational parameter during injection, influences the transient permeability change during fracture slip. We conducted a series of experiments in the laboratory using different fluid pressurization rates on a natural rough fracture in granite under a pre‐stressed state. The fracture had a high initial permeability. Our findings show that when fluid is injected into a fracture with a slight velocity‐strengthening frictional behavior, it causes slow slipping with significant permeability enhancement. The change in hydraulic aperture caused by slip velocity is the main reason for the temporary change in permeability, and this effect is modulated by fluid pressurization rate and fracture surface irregularities. Our results suggest that we can modulate the permeability of subsurface geoenergy reservoirs by controlling the fluid pressurization rate on slowly slipping fractures. Key Points We conducted fluid injection experiments on a pre‐stressed natural rough fracture in granite at different pressurization rates The velocity‐strengthening fracture exhibits slow slip accompanied by a significant increase in permeability during fluid injection Transient fracture permeability is controlled by injection‐induced slip velocity, modulated by pressurization rate and surface asperities

Essentially all hydrogeological processes are strongly influenced by the subsurface spatial heterogeneity and the temporal variation of environmental conditions, hydraulic properties, and solute concentrations. This spatial and temporal variability needs to be considered when studying hydrogeological processes in order to employ adequate mechanistic models or perform upscaling. The scale at which a hydrogeological system should be characterized in terms of its spatial heterogeneity and temporal dynamics depends on the studied process and it is not always necessary to consider the full complexity. In this paper, we identify a series of hydrogeological processes for which an approach coupling the monitoring of spatial and temporal variability, including 4D imaging, is often necessary: (1) groundwater fluxes that control (2) solute transport, mixing and reaction processes, (3) vadose zone dynamics, and (4) surface-subsurface water interaction occurring at the interface between different subsurface compartments. We first identify the main challenges related to the coupling of spatial and temporal fluctuations for these processes. Then, we highlight some recent innovations that have led to significant breakthroughs in this domain. We finally discuss how spatial and temporal fluctuations affect our ability to accurately model them and predict their behavior. We thus advocate a more systematic characterization of the dynamic nature of subsurface processes, and the harmonization of open databases to store hydrogeological data sets in their four-dimensional components, for answering emerging scientific question and addressing key societal issues.

Reliable information about the spatial distribution of surface waters is critically important in various scientific disciplines. Synthetic Aperture Radar (SAR) is an effective way to detect floods and monitor water bodies over large areas. Sentinel-1 is a new available SAR and its spatial resolution and short temporal baselines have the potential to facilitate the monitoring of surface water changes, which are dynamic in space and time. While several methods and tools for flood detection and surface water extraction already exist, they often comprise a significant manual user interaction and do not specifically target the exploitation of Sentinel-1 data. The existing methods commonly rely on thresholding at the level of individual pixels, ignoring the correlation among nearby pixels. Thus, in this paper, we propose a fully automatic processing chain for rapid flood and surface water mapping with smooth labeling based on Sentinel-1 amplitude data. The method is applied to three different sites submitted to recent flooding events. The quantitative evaluation shows relevant results with overall accuracies of more than 98% and F-measure values ranging from 0.64 to 0.92. These results are encouraging and the first step to proposing operational image chain processing to help end-users quickly map flooding events or surface waters.

Representativity and accuracy of digital rock physics (DRP) simulations depend strongly on the size of the image volume and the resolution obtained. Even with one of the fastest DRP simulation techniques like pore network modelling, simulation volumes have typically been limited to few cubic millimetres for highly resolved images. In this paper, a super-resolution technique named enhanced super-resolution generative adversarial network (ESRGAN) is used to obtain well-resolved images with large field of view and to generate micro-CT images with resolution enhancement factors of × 4 and × 8. Subsets of resulting ESRGAN images were tested against the same volume (of acquisitions resolved at high and low resolution) by comparing petrophysical properties of interest. Pore network extraction and multiphase simulation results showed that pore size distribution, porosity, permeability, drainage capillary pressure and relative permeability curves obtained using ESRGAN images were more accurate. Large images, however, pose subsequent limitations on DRP simulations as pore network extraction code needs a lot of memory to process them (usually more than 60 GB of RAM for 15003 voxels image). Thus, we present a novel stitching strategy that is developed to enable the extraction of pore networks on such large images. Several validation cases of this method are presented to test the accuracy of the results from stitched networks on single- and multiphase flow properties. Finally, our stitching tool was used to generate two large networks of 3.6 million and 9.2 million elements, respectively, from two large ESRGAN images of approximately 49003 voxels.